Method and apparatus for performing acquisition in power save mode for wireless communication systems

ABSTRACT

Techniques to efficiently attempt acquisition of a packet data system (e.g., an IS-856 system). If a terminal has acquired one or more channels in a voice/data system (e.g., an IS-2000 system), then it can attempt acquisition on channels in the packet data system that are co-located with the acquired channels in the voice/data system. Multiple acquisition modes may be used, and on-going acquisition attempts on the co-located channels may be performed using one acquisition mode at a time in order to reduce power consumption. Acquisition attempts may be performed in a “ping-pong” manner to improve the likelihood of acquisition. For a ping-pong search, an acquisition attempt is made on the most recently acquired channel prior to an acquisition attempt on each of the remaining channels. Received signal strength estimates may also be obtained for selected channels and may be used to determine whether or not to attempt acquisition on these channels.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.60/422,656 filed Oct. 30, 2002.

BACKGROUND

I. Field

The present invention relates generally to communication, and morespecifically to techniques for performing acquisition by terminalsoperating in a power save mode.

II. Background

Wireless communication systems are widely deployed to provide varioustypes of communication services such as voice, packet data, and so on.These systems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources. Examples of such multiple-access systems include codedivision multiple access (CDMA) systems, time division multiple access(TDMA) systems, and frequency division multiple access (FDMA) systems. ACDMA system may be designed to implement one or more standards such asIS-2000, IS-856, IS-95, and W-CDMA. A cdma2000 system is a CDMA systemthat may implement IS-2000 and/or IS-856. A TDMA system may be designedto implement one or more standards such as Global System for MobileCommunications (GSM). A GSM system may implement General Packet RadioService (GPRS) for packet data transmission. These various standards arewell known in the art.

Some wireless communication systems (e.g., those that implement IS-2000,W-CDMA, and GSM/GPRS) are capable of supporting voice and packet dataservices. Each type of service is characterized by a particular set ofrequirements. For example, voice service typically requires a fixed andcommon grade of service (GOS) for all users and further imposesrelatively stringent and fixed delays. In contrast, packet data servicemay be able to tolerate different GOS for different users and mayfurther be able to tolerate variable amounts of delays. To support bothtypes of service, a wireless communication system may first allocatesystem resources to voice users and then allocate any remaining systemresources to packet data users who can tolerate longer delays.

Some wireless communication systems (e.g., those that implement IS-856)are optimized for packet data transmission, which is typicallycharacterized by long periods of silence punctuated by large bursts oftraffic. For an IS-856 system, a large portion of the system resourcesmay be allocated to a single user, thereby greatly increasing the peakdata rate for the user being served.

A service provider/network operator may deploy multiple wirelesscommunication systems to provide enhanced services for its subscribers.For example, a service provider may deploy a voice/data system (e.g., anIS-2000 system) capable of providing both voice and packet data servicesfor a large geographic area. This service provider may further deploy apacket data system (e.g., an IS-856 system) capable of providing packetdata service for “hot spots”, which are areas where packet data usage isexpected to be high. The coverage areas of the two systems wouldtypically overlap, and these systems would then be considered as“overlay” systems. A multimode/hybrid terminal may then be able toreceive service from one or both of the systems depending on itslocation and the desired service.

If a terminal is mobile, then it may move into and out of the coverageareas of the individual systems as it roams about. One of the challengeswhen operating in such overlay systems is determining when to attemptacquisition of the packet data system when under the coverage of thevoice/data system. Each unsuccessful acquisition attempt of the packetdata system consumes battery power, which then reduces battery life andstandby time. When idle, the terminal may be operated in a power savemode whereby power consumption is minimized to the extent possible sothat standby time may be extended. In the power save mode, it isdesirable to attempt acquisition on the packet data system in a mannersuch that battery power is conserved while maximizing the likelihood ofacquisition.

There is therefore a need in the art for techniques to efficientlyperform acquisition by a terminal in a wireless communication system.

SUMMARY

Techniques are provided herein to efficiently attempt acquisition on awireless communication system (e.g., a packet data system, such as anIS-856 system). These techniques are especially efficient when theterminal has already acquired another wireless communication system(e.g., a voice/data system, such as an IS-2000 system).

In an aspect, information relating the voice/data system to the packetdata system is used to more efficiently attempt acquisition of thepacket data system. A terminal typically includes a preferred roaminglist (PRL) that contains entries for channels in both the voice/datasystem and the packet data system. The PRL may be defined to includeinformation indicating which channels in the packet data system are“co-located” with which channels in the voice/data system, as describedbelow. If the terminal has acquired one or more channels in thevoice/data system, then channels in the packet data system that areco-located with the acquired channels in the voice/data system may bedetermined from the PRL. Acquisition may then be attempted on a set ofco-located channels in the packet data system. Knowledge of co-locatedchannels may thus be advantageously used to limit the number of channelsto attempt acquisition on.

In another aspect, multiple (e.g., “deep” and “shallow”) acquisitionmodes are used to reduce power consumption for acquisition attempts. Thedeep acquisition mode may be designed so as to acquire a weak receivedsignal with a low signal-to-noise ratio (SNR), and the shallowacquisition mode may be designed for a received signal with a largerfrequency offset. Typically, acquisition involves searching with boththe deep and shallow acquisition modes to make sure that the terminalcan acquire the weakest possible signal while at the same time ensuringthat acquisition success is not limited by frequency offset. However,when in power-save mode, the terminal may attempt acquisition using thedeep and shallow acquisition modes in two phases. On-going acquisitionattempts on a set of channels in the packet data system may be performedusing one (deep or shallow) acquisition mode at a time to reduce powerconsumption.

In yet another aspect, acquisition is attempted on the set of channelsin a “ping-pong” manner to improve the likelihood of acquisition. For aping-pong search through a set of N+1 channels, {ch0, ch1, ch2, . . .chN}, an acquisition attempt is made on ch0 prior to an acquisitionattempt on each of the remaining channels in the set. The ping-pongsearch may attempt acquisition on these N+1 channels in the followingorder: {ch0, ch1, ch0, ch2, . . . ch0, chN}. If ch0 is the most recentlyacquired channel, and hence the most likely to have signal transmissionthan other channels, then the ping-pong search can improve thelikelihood of acquiring the packet data system.

In yet another aspect, acquisition is attempted on channels in thepacket data system based on received signal strength estimates obtainedfor these channels. A “micro search” may be performed by the terminal toobtain a received signal strength estimate for a selected channel in thepacket data system. The received signal strength estimate may then beused to determine whether or not to attempt acquisition on the selectedchannel. Micro searches may be performed in various manners, and theresults of the micro searches may also be used in various ways, asdescribed below.

Various aspects and embodiments of the invention are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 shows a deployment whereby a packet data system overlays avoice/data system;

FIG. 2 shows a flow diagram of an overall acquisition process;

FIG. 3 shows a flow diagram of a power-save acquisition process;

FIGS. 4A and 4B illustrate the power-save acquisition process with twoand three co-located channels, respectively;

FIG. 5 shows a flow diagram for one cycle in phase 4 of the power-saveacquisition process, with micro searches;

FIG. 6 illustrates one cycle in phase 4 of the power-save acquisitionprocess, with micro searches; and

FIG. 7 shows a block diagram of a terminal.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

The acquisition techniques described herein may be used by terminalsoperating in stand-alone wireless communication systems as well as byterminals operating in overlay wireless communication systems. Thesetechniques may be used for various communication systems, such asIS-2000, IS-856, IS-95, W-CDMA, GSM, and GSM/GPRS systems. For clarity,these techniques are described below for overlay communication systemscomprised of a voice/data system and a packet data system.

FIG. 1 shows a diagram of an exemplary deployment 100 whereby a packetdata system overlays a voice/data system. The voice/data system may bedeployed to provide voice and packet data services for a largegeographic area. The packet data system may be deployed to providepacket data service for “hot spots”, which are areas where packet datausage is expected to be high. The voice/data system may be an IS-2000system (which is commonly referred to as a “1x” system), a W-CDMAsystem, a GSM/GPRS system, or some other system. The packet data systemmay be an IS-856 system (which is commonly referred to as a “1xEV-DO”system or an “HDR” system) or some other system.

The voice/data system includes a number of base stations 110 that canprovide voice and packet data services for terminals located withincoverage areas 120 of these base stations. Similarly, the packet datasystem includes a number of base stations 112 that can provide packetdata service for terminals located within coverage areas 122 of thesebase stations. For simplicity, only few base stations 110 and 112 andterminals 130 are shown in FIG. 1. Base stations 110 and 112 may belocated at different sites (as shown in FIG. 1) or co-located at thesame sites. As also shown in FIG. 1, the coverage area of the packetdata system may not be contiguous and may be isolated islands withinand/or overlapping the coverage area of the voice/data system.

Base stations 110 couple to a base station controller (BSC) 140 thatprovides coordination and control for these base stations. Similarly,base stations 112 couple to a BSC 142 that provides coordination andcontrol for these base stations. BSC 140 may further couple to a packetdata serving node (PDSN) 150 that supports packet data service for thevoice/data system, and BSC 142 may further couple to a PDSN 152 thatsupports packet data service for the packet data system.

In general, a base station is a fixed station for communicating with theterminals. A base station may also be referred to as a base transceiversystem, an access point, a Node B, or some other terminology. A terminalcommunicates with the fixed stations and may also be referred to as amobile station, a remote station, a wireless communication device, auser equipment (UE), or some other terminology. A terminal may be fixedor mobile.

A mobile terminal may move throughout the coverage areas of thevoice/data system and the packet data system. For improved performance,it is desirable for the terminal to acquire and register with the packetdata system whenever it is under the coverage of this system. Theacquisition and registration process may be time consuming. By acquiringand registering with the packet data system when idle, the terminal willbe able to send and/or receive data much more quickly when initiated bythe user, which will enhance user experience and improve performance.

Due to the mobile nature of the terminal and the spotty coverage of thepacket data system, there is no simple way to determine whether or notthe terminal is under the coverage of the packet data system unless itattempts to acquire the system. However, frequent acquisition attemptscan drain battery power and shorten standby time. The acquisitiontechniques described herein may be used by the terminal to efficientlyattempt acquisition on the packet data system. These techniques areespecially efficient when the terminal is under the coverage of thevoice/data system.

FIG. 2 shows a flow diagram of an embodiment of an overall acquisitionprocess 200 that may be performed by a terminal to acquire the packetdata system.

Initially, a determination is made whether the terminal has lost thepacket data system (step 212). If the answer is ‘no’, then theacquisition process terminates. Otherwise, the terminal attemptsacquisition on a set of “co-located” channels in the packet data system(step 220). As used herein, an “acquisition attempt” on a particularchannel is a search for a signal on that channel through a designatedsearch space. This search space may comprise, for example, a range of PNphases, a range of timing offsets, a range of frequency offsets, and soon, or any combination thereof. The search space may be dependent on (1)the designs of the packet data system and/or the terminal, (2) themanner in which the packet data system is operated, and (3) possiblyother factors. The set of co-located channels may be determined asdescribed below. If the packet data system is found on one of theco-located channels (as determined in step 222), then the terminal mayperform a registration process with the packet data system via thisco-located channel (step 240) to inform the packet data system of theterminal's presence. Otherwise, the terminal enters a power-save mode(step 224).

The terminal thereafter attempts acquisition on the set of co-locatedchannels in the power-save mode (step 230). Acquisition in thepower-save mode is described in further detail below. After eachacquisition attempt on a particular co-located channel, a determinationis made whether or not the packet data system was found on this channel(step 232). If the answer is ‘yes’, then the terminal acquires thepacket data system and may perform registration with the system via thischannel (step 240). The acquisition process then terminates. Otherwise,if the packet data system was not found, then the process returns tostep 230 and the terminal continues to attempt acquisition on the set ofco-located channels. Steps 220 and 240 are described in further detailbelow.

In an aspect, information relating the voice/data system to the packetdata system is used to more efficiently search for the packet datasystem. For CDMA, a terminal typically stores a preferred roaming list(PRL) that includes a list of frequency bands and channels that theterminal may acquire. If the packet data system overlays the voice/datasystem, then each channel in the packet data system may be associated or“co-located” with a channel in the voice/data system. A channel x in thepacket data system is considered to be co-located with a channel y inthe voice/data system if a terminal that can receive a signal on channely is also likely able to receive a signal on channel x. If the coveragearea for channel y overlaps the coverage area for channel x, then thePRL may be defined to indicate that channel x is co-located with channely. This may be achieved by marking or indicating channel x as beingco-located with channel y in the PRL.

The PRL may be defined to include entries or records for channels inboth the voice/data system and the packet data system. An entry for achannel in the voice/data system may include: Channel, Frequency Band,System Identification (SID), Network Identification (NID), Co-locationTag, Preference, and Geographical Location Indicator. An entry for achannel in the packet data system may include: Channel, Frequency Band,Subnet ID, Co-location Tag, Preference, and Geographical LocationIndicator. The entry for each channel includes sufficient informationneeded to acquire that channel. The PRL may further include informationrelating channels in the voice/data system to channels in the packetdata system. This information may be provided by the serviceprovider/network operator. The information that a channel in thevoice/data system has a co-located channel in the packet data system isuseful for acquisition of the packet data system. The PRL and itscontents are described in further detail in TIA/EIA-683-B Annex C, whichis incorporated herein by reference.

If the terminal is under the coverage of the voice/data system and hasacquired one or more channels in this system, then the PRL may be usedto obtain channels in the packet data system that are co-located withthe one or more acquired channels in the voice/data system. Morespecifically, if a particular channel in the voice/data system isacquired, then the terminal can look in the PRL to determine if there isa co-located channel in the packet data system. If a co-located channelexists, then the terminal can thereafter attempt to acquire thisco-located channel. Conversely, if no co-located channels exist, thenthe terminal may save battery power by not searching for signals fromthe packet data system. Knowledge of co-located channels may thus beadvantageously used when the coverage area of the packet data systemoverlays the coverage area of the voice/data system.

The terminal may attempt acquisition on a list of zero or more channelsin the packet data system. This list may be intelligently determinedbased on the acquired voice/data system and the PRL. This list mayinclude, for example, the channels in the packet data system listed inthe PRL as being co-located with the acquired channels in the voice/datasystem, the N most recently acquired channels in the packet data system,and so on. The use of a list of co-located channels can provide improvedperformance, and is described in further detail below. This list ofco-located channels is determined based on the channel currentlyacquired by the terminal for the voice/data system.

The terminal may be designed to enter a packet data-only mode ofoperation (i.e., with only the packet data system) if a signal from thevoice/data system is not found. Alternatively, the terminal may also bedesigned to attempt acquisition of the packet data system only if thevoice/data system is found (i.e., the terminal does not search for asignal from the packet data system if a signal from the voice/datasystem is not found).

The list of co-located channels in the packet data system on which toattempt acquisition may be represented by a set S={ch0, ch1, . . . chN}.For improved acquisition performance, the co-located channels may besorted in an order determined by the amount of elapsed time since thesechannels were last acquired. The sorted set S would then include ch0 asthe channel most recently acquired among the channels in set S, andhence the most likely to be acquired, by the terminal for the packetdata system, and chN as the oldest channel acquired by the terminal orone that has never been acquired. The terminal may attempt acquisitionon the co-located channels in the set in various manners, as describedbelow.

In another aspect, multiple acquisition modes are used to reduce powerconsumption for acquisition attempts and to improve standby time. Table1 lists three acquisition modes that may be used by the terminal tosearch for signals from the packet data system. Fewer, additional,and/or different acquisition modes may also be used, and this is withinthe scope of the invention.

TABLE 1 Acquisition Mode Description Deep (D) Demodulation parametersare selected to provide improved noise immunity so that signals with lowsignal-to-noise ratios (SNRs) may be acquired. Shallow (S) Demodulationparameters are selected such that signals with larger frequency offsetsmay be acquired. Full (F) A combination of deep and shallow. A fullsearch is a deep search followed by a shallow search.

To search for a signal on a particular channel in the packet datasystem, the terminal typically detects for a pilot included in thesignal. To detect for the pilot, the signal received for that channel isconditioned and digitized to obtain complex-value data samples, whichare further processed in a manner complementary to that performed at abase station. For CDMA, the data samples are first multiplied with alocally generated pseudo-random number (PN) sequence to obtain despreadsamples. The despread samples for each time interval of Nc chips arecoherently accumulated to obtain a complex-value pilot symbol estimatefor that time interval. The squared magnitude of each pilot symbolestimate is then obtained, and Nnc magnitude-squared pilot symbolestimates are non-coherently accumulated to provide a pilot energyestimate. The pilot energy estimate is also referred to as a receivedpilot power estimate or a received signal strength estimate.

Two parameters that affect the performance of the search for signalsfrom the packet data system are the coherent integration interval (Nc)and the non-coherent integration interval (Nnc). A longer coherentintegration interval (i.e., a larger value for Nc) corresponds to moreaveraging, provides greater noise immunity, and allows for detection ofa signal with a low SNR. Conversely, a shorter coherent integrationinterval corresponds to less averaging, has reduced sensitivity, butprovides higher probability of detection for a larger frequency error.Various values may be used for Nc and Nnc for each acquisition mode, andthis is within the scope of the invention. As an example, the coherentand non-coherent integration intervals for an IS-856 system may beselected as: Nc=96 and Nnc=2 for the deep acquisition mode, and Nc=64and Nnc=2 for the shallow acquisition mode. The particular values to usefor Nc and Nnc may also be dependent on the pilot structure used by thepacket data system.

Since the timing of a signal received from the packet data system is notknown, the terminal typically searches for the pilot at various timeoffsets (or PN phases) of the locally generated PN sequence. For eachhypothesis, which corresponds to a specific PN phase, the data samplesare correlated with the locally generated PN sequence at that PN phase.The correlation is performed using the selected values for Nc and Nnc toobtain a received signal strength estimate for that hypothesis. Due tothe pseudo-random nature of the PN sequence, the correlation of the datasamples with the locally generated PN sequence should be low, exceptwhen the phase of the locally generated PN sequence is approximatelyaligned with the phase of the PN sequence in the received signal, inwhich case the correlation results in a high value.

The total time required to search for a signal on a particular channelis dependent on various factors, such as the coherent and non-coherentintegration intervals, the number of hypotheses to evaluate, and so on.In one exemplary design, the total time required to search for onechannel is approximately 820 msec using the deep acquisition mode (withNc=96 and Nnc=2), approximately 660 msec using the shallow acquisitionmode (with Nc=64 and Nnc=2), and approximately 1800 msec using the fullacquisition mode. A full search thus requires a longer time to performthan a deep or shallow search.

To reduce power consumption and increase standby time, on-goingacquisition searches for signals from the packet data system may beperformed using one (i.e., deep or shallow) acquisition mode at a time.Conventionally, each search is performed using all possible sets ofvalues for Nc and Nnc. A long period of time is then required for eachsearch, which consumes battery power and shortens standby time. Byperforming searches for one acquisition mode at a time, a shorter periodof time is required for each search without greatly impactingperformance.

Upon detecting system loss (step 212 in FIG. 2), the terminal canattempt acquisition on the set of co-located channels in the packet datasystem (step 220). For each co-located channel, the terminal may performa search using the deep, shallow, or full acquisition mode. The terminalmay cycle through the set of co-located channels one or more timesbefore declaring that the packet data system was not found (step 222)and entering the power-save mode (step 224).

FIG. 3 shows a flow diagram of an embodiment of a power-save acquisitionprocess 230 x that may be performed by the terminal to acquire thepacket data system in the power-save mode. Process 230 x may be used forstep 230 in FIG. 2. In this embodiment, process 230 x includes fourphases, which are labeled as phases 1, 2, 3, and 4. In the followingdescription, the parameters W1, W2, W3, and W4 denote the amount of timeto wait prior to the next acquisition attempt in phases 1, 2, 3, and 4,respectively. Exemplary values for these parameters are given below. Ingeneral, W1<W2<W3<W4, where W1 is the shortest wait time and W4 is thelongest wait time.

Initially, the current mode is set to the full acquisition mode (step308). For phase 1, the terminal waits W1 seconds and then attemptsacquisition on ch0, which is the most recently acquired channel in thepacket data system (step 310). The acquisition search is performed usingthe full acquisition mode. If the packet data system is found on thischannel (as determined in step 312), then the process terminates.

Otherwise, if the answer is ‘no’ for step 312, then the terminal entersphase 2 and attempts acquisition on all co-located channels in the set(step 320). The terminal waits W2 seconds prior to each acquisitionattempt in step 320. For improved performance, the terminal may attemptacquisition on the co-located channels in a “ping-pong” manner, asdescribed below. The acquisition searches are performed using the fullacquisition mode. If the packet data system is found on any of theco-located channels (as determined in step 322), then the processterminates.

Otherwise, if the answer is ‘no’ for step 322, then the terminal entersphase 3, waits for W3 seconds, and then attempts acquisition on ch0using the full acquisition mode (step 330). If the packet data system isfound on this channel (as determined in step 332), then the processterminates.

Otherwise, if the answer is ‘no’ for step 332, then the terminal entersphase 4 and performs on-going acquisition searches on all co-locatedchannels using one acquisition mode at a time (i.e., deep or shallow).This is achieved by first setting the current mode to a particular(e.g., deep) acquisition mode (step 338). The terminal then attemptsacquisition on all co-located channels using the current mode (step340). The terminal waits W4 seconds prior to each acquisition attempt instep 340. Again, for improved performance, the terminal may attemptacquisition on the co-located channels in a ping-pong manner. If thepacket data system is found on any of the co-located channels (asdetermined in step 342), then the process terminates. Otherwise, thecurrent mode is toggled (from deep to shallow, and from shallow to deep)(step 344). The process then returns to step 340, and the terminalattempts acquisition on all co-located channels using the newacquisition mode indicated by the updated current mode.

In yet another aspect, acquisition may be attempted on the co-locatedchannels in a ping-pong manner to improve the likelihood of acquisition.For a ping-pong search through the set of co-located channels, anacquisition attempt is made on ch0 prior to an acquisition attempt oneach of the other co-located channels in the set. For a set containingN+1 co-located channels {ch0, ch1, ch2, . . . chN}, a ping-pong searchmay attempt acquisition on these channels in the following order: {ch0,ch1, ch0, ch2, . . . ch0, chN}. Thus, if the set includes N+1 co-locatedchannels, then N acquisition attempts are made on ch0 and oneacquisition attempt is made on each of the other N co-located channels,ch1 through chN. Since ch0 is the most recently acquired channel in thepacket data system, the likelihood of acquiring the packet data systemvia ch0 may be much greater than any of the other co-located channels.The ping-pong search can thus improve the likelihood of acquiring thepacket data system.

A specific implementation of the system-loss acquisition process (step220 in FIG. 2) and the power-save acquisition process (process 230 x inFIG. 3) is described below. This implementation uses the ping-pongsearch for phases 2 and 4 of the power-save acquisition process.

System-Loss Acquisition

System-loss acquisition is performed after the terminal declares systemloss.

-   1. Attempt acquisition on all co-located channels-   2. Enter power-save mode

Power-Save Acquisition

Power-save acquisition is performed after failure to acquire the packetdata system using system-loss acquisition.

Phase 1

-   1. Wait W1 seconds-   2. Attempt acquisition on ch0

Phase 2

-   3. Wait W2 seconds-   4. Attempt acquisition on ch0-   5. Wait W2 seconds-   6. chx=next co-located channel in the set other than ch0-   7. Attempt acquisition on chx-   8. Go to step 3. Repeat until acquisition has been attempted on all    co-located channels in the set.

Phase 3

-   9. Wait W3 seconds-   10. Attempt acquisition on ch0-   11. Wait W3 seconds-   12. Set current mode=“deep”

Phase 4

-   13. Attempt acquisition on ch0 with current mode-   14. Wait W4 seconds-   15. chx=next co-located channel in the set other than ch0-   16. Attempt acquisition on chx with current mode-   17. Wait W4 seconds-   18. Go to step 13. Repeat until acquisition has been attempted on    all co-located channels in the set.-   19. Toggle current mode between “deep” and “shallow”.-   20. Go to step 13. Repeat until system is found.

In general, the power-save acquisition process may include any number ofphases. Furthermore, acquisition may be attempted on any number ofchannels in the packet data system for each phase. The flow diagramshown in FIG. 3 and the implementation described above representspecific embodiments of the power-save acquisition process.

For the implementation described above, acquisition is attempted on allco-located channels in a ping-pong manner for phases 2 and 4.Acquisition may also be attempted on the co-located channels in othermanners, and this is within the scope of the invention. For example,acquisition may be attempted once on each co-located channel. As anotherexample, acquisition may be attempted once or multiple times on eachco-located channel depending on, for example, the likelihood ofacquiring the channel, the amount of elapsed time since the channel waslast acquired, and so on.

FIG. 4A illustrates the power-save acquisition process with twoco-located channels {ch0, ch1}. For simplicity, the events in FIG. 4Aare not drawn to scale on the horizontal time line. Shortly after systemloss is declared for the packet data system, the terminal attemptsacquisition on the two co-located channels ch0 and ch1 using the fullacquisition mode (“F”). At the completion of these acquisition attempts,the packet data system was not acquired and the terminal enters thepower-save mode.

For phase 1 of the power-save acquisition process, the terminal waits W4seconds and then attempts acquisition on ch0. For phase 2, the terminalwaits W2 seconds prior to attempting acquisition on each of the twoco-located channels, ch0 and ch1. For phase 3, the terminal waits W3seconds, then attempts acquisition on ch0, then waits another W3seconds. The full acquisition mode is used for phases 1 through 3.

For phase 4, the terminal attempts acquisition on ch0, then waits W4seconds, then attempts acquisition on ch1, then waits W4 seconds. Thisrepresents one complete cycle through the two co-located channels in theset. The terminal then cycles through the two co-located channels insimilar manner. As indicated in FIG. 4A, the deep acquisition mode (“D”)is used for the first cycle, the shallow acquisition mode (“S”) is usedfor the second cycle, the deep acquisition mode is used again for thethird cycle, and so on.

FIG. 4B illustrates the power-save acquisition process with threeco-located channels {ch0, ch1, ch2} and ping-pong search. Shortly afterdeclaring system loss, the terminal attempts acquisition on the threeco-located channels, ch0, ch1, and ch2, using the full acquisition mode.The terminal enters the power-save mode at the completion of theseacquisition attempts when the packet data system was not acquired.

For phase 1 of the power-save acquisition process, the terminal waits W1seconds and then attempts acquisition on ch0. For phase 2, the terminalwaits W2 seconds, then attempts acquisition on ch0, then waits W2seconds, then attempts acquisition on ch1, then waits W2 seconds, thenattempts acquisition on ch0, then waits W2 seconds, then attemptsacquisition on ch2. This represents one complete cycle through the threeco-located channels. For this cycle, the terminal attempts acquisitiontwice on ch0 and once on each of the other two co-located channels, ch1and ch2. For phase 3, the terminal waits W3 seconds, then attemptsacquisition on ch0, then waits another W3 seconds. Again, the fullacquisition mode is used for phases 1 through 3.

For phase 4, the terminal cycles through the three co-located channelsin a manner similar to that described above for phase 2. The deepacquisition mode is used for the first cycle (as indicated in FIG. 4B),the shallow acquisition mode is used for the second cycle (not shown inFIG. 4B), and so on.

The four phases for the power-save acquisition process are used to coverdifferent operating scenarios. For phase 1, acquisition is attempted onthe most recently acquired channel, ch0, W1 seconds after system loss isdeclared. Phase 1 is useful for an occasional loss of system due tofade. For phase 2, acquisition is attempted on all co-located channelswith W2 seconds of wait time between acquisition attempts. Phase 2 isuseful for two scenarios. The first scenario is a temporary loss ofcoverage, such as when the terminal is blocked from receiving signal fora couple of seconds. The second scenario is when the terminal moves fromone frequency coverage to another. In this case, the terminal willsearch all co-located channels in phase 2 and will find the new channelto which it has moved to, without too much delay. The search through allco-located channels provides a high degree of confidence that coverageis indeed lost before proceeding to the next phase. For phase 3,acquisition is attempted on the most recently acquired channel, ch0,after a longer wait of W3 seconds. Phase 3 is useful for longer loss ofcoverage (e.g., driving through a tunnel) and has been shown to provideimproved acquisition performance in many cases. By the time the terminalenters phase 4, there is a high degree of confidence that the terminalhas no packet data system coverage. Hence, in order to save power, inphase 4, acquisition is periodically attempted with larger wait time onthe co-located channels in an on-going process to acquire the packetdata system.

The values for the parameters W1, W2, W3, and W4, which are used forphases 1, 2, 3, and 4, respectively, are selected to provide goodacquisition performance as well as long standby time. The specificvalues to use are dependent on various factors such as the desiredresults, the operating environment, the terminal design, and so on. Forexample, one set of values may be used to achieve long standby time, asecond set of values may be used to achieve faster acquisition time, athird set of values may be used to achieve a compromise between longstandby time and fast acquisition time, and so on. The values for W1,W2, W3, and W4 may be fixed and stored within the terminal.Alternatively, these values may be configured, for example, viaover-the-air signaling.

Table 2 lists exemplary values for the parameters W1, W2, W3, and W4.Other values may also be used, and this is within the scope of theinvention.

TABLE 2 Parameter Value W1  2 seconds W2  6 seconds W3  30 seconds W4420 seconds

Once the terminal acquires the packet data system but is idle, it mayenter a sleep mode whereby most of the circuitry is powered down toconserve battery power. In the sleep mode, the terminal periodicallywakes up to check for pages and messages sent on an overhead channel.The awake time is determined by the total time required to warm up andtune the RF circuitry, search for the overhead channel, and process anddecode the overhead channel. The sleep cycle duration (i.e., the timeduration between consecutive awake periods) may be fixed or configuredfor the terminal to provide the desired sleep performance.

The value for W4 may be selected to achieve standby time performancethat is comparable to sleep performance. If the awake time is 80 msecand the sleep cycle duration is 40 seconds in the sleep mode, then theawake percentage is 0.080/40=0.2%. If each acquisition attempt on achannel in the packet data system takes approximately 800 msec, then toachieve the same 0.2% awake percentage the value for W4 may be selectedto be approximately 0.80/0.002=400 seconds.

Conventionally, the wait times for different phases of the acquisitionprocess are typically much less than 400 seconds. For example, waittimes of 10, 60, and 180 seconds may be used for phases 1, 2, and 3,respectively, of a 3-phase acquisition process. For each phase,acquisition is normally attempted multiple times on all channels in thesystem. Furthermore, a full search (e.g., both deep and shallowsearches) is typically performed for each channel. This combination ofshort wait time, searching through all channels, and full search foreach channel can result in significantly shorter standby time, which ishighly undesirable for mobile application. A long wait time may be usedfor W4 without greatly sacrificing performance because the terminal canobtain service from the voice/data system.

An acquisition attempt on a given channel can take a relatively longtime (e.g., approximately 800 msec, for just the deep or shallowacquisition mode for an exemplary design). A received signal strengthestimate may be obtained for a channel in a much shorter amount of time(e.g., approximately 30 to 40 msec, for an exemplary terminal design).This is because accurate timing and frequency need not be achieved toobtain a received signal strength estimate for a channel. A receivedsignal strength estimate that is sufficiently high would indicate a highlikelihood of a signal being present on the channel. However, a receivedsignal strength estimate that is low may not accurately indicate thepresence or absence of a signal on the channel. This is because a weaksignal may still be acquired once timing and frequency lock have beenachieved.

In yet another aspect, acquisition is attempted on the co-locatedchannels based on received signal strength estimates obtained for thesechannels. A “micro search” may be performed by the terminal to obtain areceived signal strength estimate for a channel. Micro searches may beperformed and used in various manners in the power-save mode to improvestandby time, as described below.

The result of a micro search for a given channel may be used todetermine whether or not to attempt acquisition on that channel. Aterminal in a CDMA system may be designed with the capability to recovera signal with received power ranging from −25 dBm to −105 dBm. Thereceived signal strength estimate for the co-located channel may becompared against one or more thresholds, and acquisition may or may notbe attempted based on the result of the comparison.

As an example, two thresholds of −65 dBm and −85 dBm may be used. If thereceived signal strength estimate exceeds −65 dBm, which indicates ahigh likelihood of a signal being present on the channel, thenacquisition may be attempted on this channel using the full acquisitionmode. If the received signal strength estimate is greater than −85 dBmbut less than −65 dBm, which indicates a good likelihood of a signalbeing present on the channel, then acquisition may be attempted on thischannel using the deep or shallow acquisition mode. As another example,a single threshold of −75 dBm may be used. If the received signalstrength estimate is greater than −75 dBm, then acquisition may beattempted on the channel using the deep, shallow, or full acquisitionmode. In general, if the received signal strength estimate is greaterthan a particular threshold, then acquisition may be attempted on thischannel, without having to wait for the expiration of the wait time.

The micro searches may be performed in various manners. In oneembodiment, micro searches are performed during the wait time between“scheduled” acquisition attempts. The normal search schedule hasacquisition being attempted on the co-located channels every W4 seconds.These may be considered as scheduled acquisition attempts. One or moremicro searches may be performed for one or more selected channels duringthe wait time W4 between consecutive scheduled acquisition attempts. Forexample, a micro search may be performed every Wm seconds (e.g., 30seconds) during the wait time W4, and the co-located channels in the setmay be cycled through. The results of these micro searches may be usedto invoke additional acquisition attempts.

In another embodiment, a micro search is performed at the end of (orconcurrent with) each scheduled acquisition attempt to obtain a receivedsignal strength estimate for the next co-located channel to be searchedor a randomly selected co-located channel. For example, a receivedsignal strength estimate may be obtained for ch1 after the acquisitionattempt on ch0 is completed.

FIG. 5 shows a flow diagram of an embodiment of a process 340 x that maybe used for one cycle in phase 4 of the power-save acquisition process.Process 340 x may be used for step 340 in FIG. 3. In this embodiment,process 340 x performs a scheduled acquisition attempt on a co-locatedchannel every W4 seconds using the current mode, which may be the deepor shallow acquisition mode. Process 340 x further performs a microsearch every Wm seconds between scheduled acquisition attempts, whereWm<W4.

At the start of the cycle, an index j is initialized to one (i.e., j=1)(step 510). This index is used to determine the next co-located channelto attempt acquisition on under the normal search schedule. A variablechx is then set to ch0 (step 512). The variable chx indicates the nextco-located channel to attempt acquisition on under the normal searchschedule.

The terminal then attempts acquisition on chx using the current mode(step 520). If the packet data system is found on this channel (asdetermined in step 522), then the process terminates. Otherwise, theterminal waits Wm seconds (step 530) and then performs a micro searchfor a selected channel, chy, to obtain a received signal strengthestimate for this channel (step 532). The selected channel may be thenext co-located channel to attempt acquisition on under the normalsearch schedule (which may be determined as shown in steps 546 and 550)or a randomly selected channel. Alternatively, the co-located channelsin the set may be cycled through by the micro searches, starting withch0 or ch1, and the selected channel may be the next co-located channelin the set to perform the micro search on.

The received signal strength estimate for the selected channel may becompared against one or more thresholds (step 534). The terminal mayattempt acquisition on the selected channel if the received signalstrength estimate exceeds the threshold(s) (step 540). Multiplethresholds may be used, for example, to determine which acquisition modeto use for the selected channel, as described above. If the packet datasystem is found on this selected channel (as determined in step 542),then the process terminates.

Otherwise, a determination is made whether or not the elapsed time isgreater than W4 seconds (step 544). If the answer is ‘no,’ then theprocess returns to step 530 to perform the next micro search. Otherwise,if the elapsed time exceeds W4 seconds, then the index j is incremented(step 546). If the index j is greater than 2N (as determined in step548), which indicates that acquisition has been attempted on allco-located channels in the set, then the process terminates. Otherwise,acquisition is attempted on the next co-located channel. For theping-pong search, the variable chx is set to ch0 if the index j is oddand to ch(j/2) if the index j is even. The process then returns to step520 to attempt acquisition on chx.

FIG. 6 illustrates one cycle in phase 4 of the power-save acquisitionprocess, with micro searches. For this embodiment, the set includesthree co-located channels {ch0, ch1, ch2}, and micro searches areperformed for all channels in the set.

For this cycle, the terminal first attempts acquisition on ch0 using thecurrent mode M, where M is either deep or shallow. For each Wm secondsthereafter, the terminal performs a micro search for the next co-locatedchannel in the set, starting with ch0 (as shown in FIG. 6) or a randomlyselected channel. After W4 seconds, the terminal attempts acquisition onch1. For each Wm seconds after the completion of the acquisition attempton ch1, the terminal performs a micro search for the next co-locatedchannel in the set, starting with ch0, a randomly selected channel, orthe channel after the last one for which a micro search was performed.Thereafter, the acquisition attempts on ch0 and ch2 and the microsearches during the wait times between these acquisition attempts may beperformed in similar manner, as shown in FIG. 6.

The acquisition techniques described herein may be used by a hybridterminal operating in overlay communication systems (e.g., IS-2000 andIS-856 systems). In this case, information relating the channels in thetwo systems may be used to streamline the acquisition process, asdescribed above. These acquisition techniques may also be used by aterminal operating in a stand-alone system (e.g., an IS-856 system). Inthis case, the set of channels on which to attempt acquisition may bedetermined in various manners. For example, the set may include the Nmost recently acquired channels, the N channels acquired within the lastT seconds, the N channels most likely to be acquired, the N availablechannels, and so on, where N can be any integer zero or greater. Thevalues for the parameters W1 through W4 may be selected to provide thedesired performance for a terminal operating in the stand-alone system,which may be different from the values used for overlay systems. Microsearches may also be performed on the channels in the system to improveacquisition performance while minimizing impact to standby time.

FIG. 7 shows a block diagram of an embodiment of a terminal 130 xcapable of communicating with multiple wireless communication systems(e.g., IS-2000 and IS-856 systems). Terminal 130 x may be any one of theterminals shown in FIG. 1, and may be a cellular phone, a handset, awireless device, a modem, or some other device.

At terminal 130 x, the forward link signals transmitted by the basestations in multiple systems are received by an antenna 712 and providedto a receiver unit (RCVR) 714. The received signal from antenna 712typically includes one or more instances of the forward link signaltransmitted by each of multiple base stations. Receiver unit 714conditions (e.g., filters, amplifies, and frequency downconverts) thereceived signal and digitizes the conditioned signal to provide datasamples. The frequencies used by receiver unit 714 for the frequencydownconversion are typically dependent on the channel being processed oracquired by the terminal.

A demodulator (Demod) 716 then processes the data samples in accordancewith the systems being received. Demodulator 716 may implement a rakereceiver that is capable of processing multiple signal instances in thereceived signal to obtain pilot estimates and demodulated symbols foreach of one or multiple base stations. For a CDMA system, the processingby demodulator 716 to obtain pilot estimates for a particular channelmay include (1) despreading the data samples with a PN sequence assignedto the channel being recovered, (2) decovering the despread samples witha channelization code for the pilot channel (which is typically asequence of all zeros) to obtain decovered pilot symbols, and (3)filtering the decovered pilot symbols to provide the pilot estimates.For a CDMA system, the processing by demodulator 716 to obtaindemodulated symbols for a particular channel may include (1) despreadingthe data samples with the PN sequence assigned to the channel beingrecovered, (2) decovering the despread samples with a channelizationcode for each traffic channel being recovered, and (3) data demodulatingthe decovered symbols with the pilot estimates to obtain the demodulatedsymbols, which are estimates of the symbols transmitted on the channelby the base station. A decoder 718 further processes (e.g.,deinterleaves and decodes) the demodulated symbols to provide decodeddata, which may be stored in a data buffer 720.

Demodulator 716 and/or a controller 730 may further process the pilotestimates to obtain the received signal strength estimate for thechannel, which may then be used to determine whether or not to attemptacquisition on that channel, as described above.

An acquisition control unit 734 controls acquisition by the terminal,initiates acquisition attempts on channels in the packet data system,and may implement the acquisition processes described above. Unit 734may determine the list of co-located channels in the packet data systemon which to attempt acquisition, based on the PRL stored in a memoryunit 732 and the one or more channels acquired for the voice/datasystem, as described above. Unit 734 may then initiate acquisitionattempts on the co-located channels based on (1) timing informationprovided by a timer 736, (2) received signal strength estimates andsearch results provided by demodulator 716, and (3) possibly otherinformation.

Controller 730 may direct the operation of various processing unitswithin terminal 130 x. Memory unit 732 may store data and program codesused by various processing units within terminal 130 x and may furtherstore the PRL. A bus 740 may be used to provide the interface betweenvarious processing units within terminal 130 x. Controller 730 may alsoimplement acquisition control unit 734.

The acquisition techniques described herein may be implemented byvarious means. For example, these techniques may be implemented inhardware, software, or a combination thereof. For a hardwareimplementation, the elements used to implement the acquisitiontechniques may be implemented within one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, other electronic units designed toperform the functions described herein, or a combination thereof.

For a software implementation, the techniques described herein may beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The software codes may be storedin a memory unit (e.g., memory unit 732 in FIG. 7) and executed by aprocessor (e.g., controller 730). The memory unit may be implementedwithin the processor or external to the processor, in which case it canbe communicatively coupled to the processor via various means as isknown in the art.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A wireless device comprising: a control unit operative to obtaininformation for an acquired first wireless communication systemimplementing a first communication standard, determine one or morechannels in a second wireless communication system implementing a secondcommunication standard based on the information obtained for the firstsystem implementing the first communication standard, and initiateacquisition attempts on the one or more channels in the second system,wherein the one or more channels in the second system are determinedbased on the information obtained for the first system to limit thenumber of channels to attempt acquisition for the second system; and ademodulator operative to process a received signal in accordance withthe first standard when receiving the first system and in accordancewith the second standard when attempting acquisition on the one or morechannels in the second system as indicated by the control unit.
 2. Thedevice of claim 1, farther comprising: a memory unit operative to storea roaming list with entries for channels in the first system, entriesfor channels in the second system, and information indicating whichchannels in the second system are co-located with which channels in thefirst system.
 3. The device of claim 1, wherein the information obtainedfor the first system indicates one or more channels in the first systemwhich the device has acquired, and wherein the one or more channels inthe second system are co-located with the one or more channels in thefirst system.
 4. The device of claim 1, wherein the one or more channelsin the second system are sorted in an order determined by amount ofelapsed time since the one or more channels were last acquired by thedevice.
 5. The device of claim 1, wherein the control unit is operativeto forego initiating acquisition attempts if no channels in the secondsystem are determined based on the information obtained for the firstsystem.
 6. The device of claim 1, wherein the control unit is operativeto initiate acquisition attempts on the one or more channels using aplurality of phases, each phase being associated with a respective waittime, and wherein acquisition attempts are initiated on at least one ofthe one or more channels for each of the plurality of phases.
 7. Thedevice of claim 1, wherein the first system supports voice and packetdata services and the second system supports packet data service.
 8. Thedevice of claim 1, wherein the first system is an IS-2000 system and thesecond system is an IS-856 system.
 9. A wireless device comprising: acontrol unit operative to obtain information for an acquired firstwireless communication system, determine one or more channels in asecond wireless communication system based on the information obtainedfor the first system, and initiate acquisition attempts on the one ormore channels in the second system using a plurality of phases, eachphase being associated with a respective wait time, wherein acquisitionattempts are initiated on at least one of the one or more channels foreach of the plurality of phases, and wherein the control unit isoperative to wait for a wait time of more than 180 seconds prior toinitiating an acquisition attempt in a last phase of the plurality ofphases; and a demodulator operative to process the one or more channelsas indicated by the control unit.
 10. An apparatus comprising: means forobtaining information for an acquired first wireless communicationsystem implementing a first communication standard; means fordetermining one or more channels in a second wireless communicationsystem implementing a second communication standard based on theinformation obtained for the first system implementing the firstcommunication standard and for limiting the number of channels toattempt acquisition for the second system based on the informationobtained for the first system; and means for initiating acquisitionattempts on the one or more channels in the second system.
 11. Theapparatus of claim 10, further comprising: means for storing a roaminglist with entries for channels in the first system, entries for channelsin the second system, and information indicating which channels in thesecond system are co-located with which channels in the first system.12. The apparatus of claim 10, wherein the information obtained for thefirst system indicates one or more acquired channels in the firstsystem, and wherein the one or more channels in the second system areco-located with the one or more acquired channels in the first system.13. The apparatus of claim 10, further comprising: means for processinga received signal in accordance with the first standard when receivingthe first system; and means for processing the received signal inaccordance with the second standard when attempting acquisition on theone or more channels in the second system.
 14. A method of acquisition,comprising: obtaining information for an acquired first wirelesscommunication system implementing a first communication standard;determining one or more channels in a second wireless communicationsystem implementing a second communication standard based on theinformation obtained for the first system implementing the firstcommunication standard and limiting the number of channels to attemptacquisition for the second system based on the information obtained forthe first system; and initiating acquisition attempts on the one or morechannels in the second system.
 15. The method of claim 14, wherein theinformation obtained for the first system indicates one or more acquiredchannels in the first system, and wherein the one or more channels inthe second system are co-located with the one or more acquired channelsin the first system.
 16. The method of claim 14, further comprising:processing a received signal in accordance with the first standard whenreceiving the first system; and processing the received signal inaccordance with the second standard when attempting acquisition on theone or more channels in the second system.
 17. A processor readablemedia for storing instructions operable in a wireless device to: obtaininformation for an acquired first wireless communication systemimplementing a first communication standard; determine one or morechannels in a second wireless communication system implementing a secondcommunication standard based on the information obtained for the firstsystem implementing the first communication standard and limit thenumber of channels to attempt acquisition for the second system based onthe information obtained for the first system; and initiate acquisitionattempts on the one or more channels in the second system.
 18. Theprocessor readable media of claim 17, and further for storinginstructions operable to: initiate processing of a received signal inaccordance with the first standard when receiving the first system; andinitiate processing of the received signal in accordance with the secondstandard when attempting acquisition on the one or more channels in thesecond system.
 19. The processor readable media of claim 17, and furtherfor storing instructions operable to: receive a roaming list withentries for channels in the first system, entries for channels in thesecond system, and information indicating which channels in the secondsystem are co-located with which channels in the first system.
 20. Theprocessor readable media of claim 17, wherein the information obtainedfor the first system indicates one or more acquired channels in thefirst system, and wherein the one or more channels in the second systemare co-located with the one or more acquired channels in the firstsystem.